1. Field of the Invention
This invention relates to apparatus for differential pressure forming an article in a sheet of thermoplastic material at a forming and trimming station and then trimming the article integrally formed with the sheet at the forming and trimming station. More particularly, this invention relates to differential pressure forming method and apparatus including a pair of differential pressure molds at a forming and trimming station, wedge mechanism for incrementally indexing a trim die, mounted on one of the molds, towards an opposing trim die, mounted on the other of the molds, to trim the article from the sheet at the forming and trimming station.
2. Description of the Prior Art and Objects
Apparatus such as that disclosed in U.S. Pat. No. 3,664,791, granted to G.W. Brown, on May 23, 1972, which is incorporated herein by reference, has been provided heretofore for successively delivering a heated thermoplastic sheet to a heating station and then to a forming station at which molds engage the sheet to differentially pressure form an article in the sheet.
Apparatus such as that disclosed in U.S. Pat. No. 4,313,358, granted to Gaylord W. Brown on Feb. 2, 1982, which is incorporated herein by reference, has been provided heretofore for trimming articles integrally formed in a thermoplastic sheet at a trimming station which is downstream of the forming station.
Another differential pressure forming machine is illustrated in U.S. Pat. No. 3,346,923, issued to G.W. Brown, et al on Oct. 17, 1967, which is incorporated herein by reference, and includes a pair of opposed cooperating molds for engaging opposite sides of a heated thermoplastic sheet to differentially pressure form an article in the sheet. This prior art machine includes a female mold cavity on one side of the sheet and a male punch and pressurized air on the other side of the sheet for urging the sheet into the mold cavity.
It has been found that when pressurized air is introduced to the molds, the molds tend to separate and thus compressible o-rings have been mounted on the confronting portions of the molds for maintaining a seal between the molds and the thermoplastic sheet when the molds slightly separate under the force of the pressurized air.
Other differential pressure forming machines are disclosed in the U.S. Patent granted to G.W. Brown, et al on Oct. 17, 1967 and U.S. Pat. No. 3,496,257 issued to G.W. Brown on Feb. 17, 1970, which are incorporated herein by reference.
Differential pressure forming machines have included trim dies at the forming and trimming station for trimming the parts at the forming and trimming station, however, the prior machines included direct acting, hydraulically operated cylinders and/or cams for moving the trim mechanism to sever the article from the sheet.
Because of the rather substantial force required to move the molds between spaced apart, open positions and closed positions and to hold the molds closed when pressurized air is admitted to the molds, these prior art hydraulically operated cylinders are quite large and thus relatively expensive. Accordingly, it is an object of the present invention to provide differential pressure forming apparatus and method for forming and trimming articles in a sheet of thermoplastic material which is less expensive than the prior art machines.
Another object of the present invention to provide apparatus for differential pressure forming an article in a sheet of thermoplastic material at a forming and trimming station and severing the article from the sheet of material at the forming and trimming station and which eliminates the necessity of a hydraulically operated cylinder for moving one of the trim dies toward the other of the trim dies.
A further object of the present invention to provide apparatus for differential pressure forming an article in a sheet of thermoplastic material and severing the trimmed article from the sheet and which eliminates the necessity of o-rings for sealing the molds to the sheet.
It is a still further object of the present invention to provide apparatus for differential pressure forming an article in a sheet of thermoplastic material and severing the article from the sheet at a forming and trimming station and which positively clamps the molds to the sheet during the differential pressure forming operation and incrementally indexes opposing trim dies together after the forming operation to sever the sheet at the forming and trimming station.
Another object of the present invention is to provide apparatus for differential pressure forming the article in a sheet of thermoplastic material and severing the article from the sheet at a forming and trimming station including mechanism moveable in a path transverse to the path of travel of the molds for wedging trim dies together to sever the article at the forming and trimming station.
Yet another object of the present invention is to provide apparatus of the type described for forming an article in a sheet of thermoplastic material and severing the article from the sheet at a forming and trimming station and incorporates pneumatically operated cylinders for moving the trim actuator.
Still another object of the present invention is to provide apparatus for differential pressure forming an article in a sheet of thermoplastic material and severing a sheet at a forming trim station including a wedge which is moveable in a path transverse to the path of travel of the trim die and a roller engageable by the wedge for moving at least one of the trim dies to sever the article formed in the sheet.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.